Beater for hammer mills

ABSTRACT

A beater for an impact pulverizer mill which has replaceable head hammers and means securely attaching the head to the arm in a pre-set position.

United States Patent 11 3,901,452 Loevenich Aug. 26, 1975 [54] BEATER FOR HAMMER MlLLS FOREIGN PATENTS OR APPLICATIONS lnvemofl Josef Loevenich, Leverkusen, 1,215,485 4/1966 Germany 241/197 Germany [73] Assignee: Babcock & Wilcox Limited, London, Primary Examiner Roy Lake England Assistant Examiner-E. F. Desmond [22] Filed; Oct 5, 1973 Attorney, Agent, or Firm-J. M. Maguire [21] Appl. No.: 404,055

a [57] ABSTRACT [52] US. Cl. 241/197 [51] Int. Cl. B02c 13/28 A beater for an impact pulverizer mill which has re- [58] Field of Search 241/ I97 placeable head hammers and means securely attaching the head to the arm in a pre-set position. [56] References Cited UNITED STATES PATENTS 1 Claim, 13 Drawing Figures 2,404,775 7/1946 Ehmann 241/197 PAE'ENTED AUB26 ms 3, 9O 1 #152 am 1 OF 4 PATENTED AUBZBIS'IS 3.901 ,452

SPZEET 3 OF {I BEATER FOR HAMMER MILLS BACKGROUND OF THE INVENTION This invention pertains to a beater for an impact pulverizer mill which has replaceable head hammers. The head is equipped at the rear with a hollow cove which has two slip-in grooves and two bearing depressions. The arm is provided with two pivots (studs) in form of a T which after insertion towards the bearing depressions in the head, flexibly connect the head to the arm. The connection is secured against slipping-out and is protected from the feed material by the skirt-like forward part of the head. The connection forms a good strong joint. A worn-out head can easily be disconnected because the slip-in grooves are accessible for cleaning. However, the connection has the disadvantage that the pivots wear out, to that during replacement of a head it is often necessary to repair the arm or also to replace it.

The wear of the pivot is a result of continuous swinging of the head around the pivot. The centrifugal force keeps the head and the arm elastically in the radial tension position. The impact of the feed material gives the impulse to swings. The short distance of the center of gravity of the head from the pivot and the presence of the centrifugal force explain the high swinging frequency and the large specific bearing pressure, both of which cause the frictional wear.

A beater is already known as shown in the German Patent DT-PS l 198 175 which has a head with semicylindrical bearing depressions which are connected to the arm either in a pivoting mode or rigidly. A projection of an insert piece is inserted into a slit in the arm to hinder the swinging of the head. The construction has the disadvantage that the cross-section of the pivot is weakened by the slit and the continuity of the bending stress fibers is disturbed. Also, due to corrosions it is very difficult to remove the insert piece and to disengage the head from the arm.

A beater is also known, see German Patent DT-PS 848, 006, which has a head rigidly connected to the arm. The connection has the disadvantage that the flat projections on the arm are only stressed on the inside by the centrifugal force along the connecting line be tween the center of gravity of the beater and the center of gravity of the head. The flat projections have the smallest bending cross-section just in that direction. In addition, although the head can be easily installed, there are great difficulties to remove it from the arm because the slots on the head are not accessible and can not be cleaned.

The object of this invention is to insure an easy replacement of the head and at the same time to avoid the swinging of the head around the axis of the pivots and thereby prevent the wear of the pivots.

SUMMARY OF THE INVENTION The solution according to the invention is to deepen the bearing recesses and to provide two opposing flat surfaces that are in contact with two axial surfaces on the pivot and are arranged nearly perpendicular to the neutral bending fibers of the pivot, and at least one of the surfaces on the pivot is flat.

The location of the surfaces on the pivot is so chosen, that the originally cylindrical pivot is not weakened in the direction of the bending stresses because the ten sion and compression fibers remain continuous.

Through the contact of the flat surfaces of the pivots and the head a stiff connection is achieved which prevents swinging of the head around the axis of the pivots thus avoiding the wear of the pivots.

The flat surfaces of the pivot can be arranged parallel so that the head is held in position on the pivot in a wrench-like fashion.

The flat surfaces of the pivot can be inclined to form an acute angle in the direction of the arm, so that the pivots become wedged between the surfaces in the head due to the action of the centrifugal force. However, due to the inclination the surfaces can be easily disengaged, for example, through a hammer blow on the worn-out head.

The upstream surfaces of the pivots in the direction of rotation can be arranged so that one surface of each pivot and the end of the arm form a single extended flat plane while the cross-section of the pivot receives the shape of a tear drop. This way a three point contact is achieved which prevents swinging of the head. The head contacts the arm once at the top of the extended front surface and also at the stem of the arm. Between these two contact points of the head the arm touches the head again at the two pivots which contact the rear flat surfaces of the deepened bearing recesses in the head. A torsional stress of the pivots is also avoided through the prevention of swinging. The streamlined part of the pivots makes the assembly and disengagement of head and arm easier. A hump may be provided on the head at the contact point with the stem in order to allow for adjustment of the cast head by grinding.

The advantages of the invention is, that in order to replace the heads in a hammer mill, which usually are experiencing the largest wear, it is not necessary to remove the rotor nor is it necessary to disassemble the arms from the shaft. This represents a large saving. This advantage can be achieved through the increase of the service life of the arms due to the reduction in wear of the pivots.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an armpivot.

FIG. 2 is a plan view of the arm-pivot.

FIG. 3 is a cross section of the hammer head.

FIG. 4 is a cross section of the head arm-pivot arrangement.

FIG. 5 is a side view of an alternative arm-pivot.

FIG. 6 is a plan view in accordance with FIG. 5.

FIG. 7 is a cross section of the hammer head in accordance with FIG. 5.

FIG. 8 is a cross section of the head arm-pivot arrangement in accordance with FIG. 5.

FIG. 9 is a side view of a further embodiment of the arm-pivot.

FIG. 10 is a plan view in accordance with FIG. 9.

FIG. 11 is a cross section of the hammer head in accordance with FIG. 9.

FIG. 12 is a cross section of the head arm-pivot arrangement in accordance with FIG. 9.

FIG. 13 is a rear view of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Application examples of the inventions are depicted on the attached drawings and are further described in the following paragraphs. The figures show a part of the beater with the head 1 in cross section and the arm 2 in view. The stem (not shown) of the arm 2 is attached to the rotating shaft of a high speed impact pulverizer through a hinged connection. The shaft rotates in the direction of the arrow A.

The cast head 1 is provided with a hollowed cove 3, which has two insertion grooves 4 arranged towards the rear in the opposite direction to the arrow A. Each insertion groove 4 has a bearing recess 5 and a depression 6. The hollow cove 3 is protected by the skirt-like part 7 of the head. The forged arm 2 is provided with two pivots 8. The pivots 8 fit into the bearing recesses 5 and are secured against falling-out through extensible bars 9 which originally were bent in the form of a V and through straightening have been expanded into the depression 6.

The FIGS. 1 to 4 show, that according to the invention, the bearing recesses 5 are deeper than half cylinders, so that two additional opposing flat surfaces 10 and 11 are provided. The pivots 8 are also provided with two axial surfaces 12 and 13 which are located about perpendicular to the neutral bending fibers 14 of the pivots. The pivots are exposed to bending due to centrifugal force in the direction of the force arrows C and D. The neutral bending plane B-B goes through the center of gravity of the pivot cross sections. In this example the planes 12 and 13 are fiat and parallel so that according to FIG. 4 the planes l and 12 as well as planes 11 and 13 are touching.

FIGS. to 8 show an example where planes 12 and 13 of the pivot 8 are also flat, but are inclined at an acute angle'l5 toward the direction of the arm.

The touching of plane with plane 12 and plane 11 with plane 13 prevent a pivoting movement of the head 1.

FIGS. 9 to 12 show an example in which the arm 2 rests on the skirt-like part 7 of the head 1. The surface 13 of the pivot 8 is arranged so that it forms a single fiat plane with the end of arm 2. The cross section of the pivot 8 has the shape of a tear drop and the elongated side is flush with the arm. This results in a three point support that prevents a swinging movement of the head 1. The elongated plane 13 of the arm and pivot touches the plane 11 of the bearing-recess which is extended to the skirt-like part 7 of the head 1. Simultaneously the arm 2 touches also the skirt-like part 7 of the head 1 at the point 16. Also, the plane 12 of the pivot 8 touches the flat plane 10 of the bearing recess 5. This way a three point contact is formed at the touching pairs of surfaces (11, 13), (2, l6) and (10, 12). At the location 16 a hump is provided on the part 7 of the head which can be easily used for fitting-in the cast head into the forged arm by slight grinding of the hump.

FIG. 13 is a rear view of the present invention showing the hammer head 1 and the arm 2 locked in their operative position, and also, showing the extensible bar 9 inserted into the depressions 6.

In order to replace the head it is first necessary to remove the worn-out head from the arm. For this purpose the hollowed cove 3 is first cleaned and the extensible bar 9 is bent so that it comes out of the depressions 6. Then a knock with a hammer on the head loosens the contact surfaces 10 and 12. The head is now pushed in the direction of the arrow B and swung-out in the direction of the arrow F so that the pivots 8 glide and turn over the area 17 of the insertion grooves 4. Finally, the worn-out head is removed in 3 turned position and is replaced by a new one, using a reversed sequence of assembly.

To replace the heads in a mill it is necessary to open only one casing door that gives access in radial direction to the mill rotor. All work steps in the replacement of heads are performed in the radial direction of the mill rotor.

A long service time of the arms is obtained due to the reduction of the swinging frequency and swinging amplitude of the arms achieved by the large distance of the center of gravity of the beater from the center of the hinged connections of the arms with the rotor shaft. The space conditions of this hinged connection permits the use of thick and long hinged pins which reduce the specific pressure on the bearing surface thus reducing the material wear of the arm.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A beater for a hammer mill including a rotatable arm with a replaceable cast head at one end thereof in which the head is provided with a hollowed cove having two insertion ggrooves directed towards the rear of the head and two bearing recesses, and with the arm provided with two pivots resting in the bearing recesses and secured against falling out, characterized by each of the pivots having two flat surfaces, bearing recesses each having two flat surfaces adapted to contact the' corresponding surfaces on a corresponding pivot, the arrangement of the surfaces on the pivots being formed in such a way that the extension of the surfaces in the direction of the arm form a single surface and the cross section of the pivots have a tear drop-like shape, a hump of predetermined dimension being provided on the head inside of the hollow cove at a point where the head contacts the arm, the pivots being constructed and arranged, when they are inserted into the grooves and rotated relative to the recesses into their operative position in the recesses, to prevent relative rotational movement between the arm and the head. 

1. A beater for a hammer mill including a rotatable arm with a replaceable cast head at one end thereof in which the head is provided with a hollowed cove having two insertion ggrooves directed towards the rear of the head and two bearing recesses, and with the arm provided with two pivots resting in the bearing recesses and secured against falling out, characterized by each of the pivots having two flat surfaces, bearing recesses each having two flat surfaces adapted to contact the corresponding surfaces on a corresponding pivot, the arrangement of the surfaces on the pivots being formed in such a way that the extensIon of the surfaces in the direction of the arm form a single surface and the cross section of the pivots have a tear drop-like shape, a hump of predetermined dimension being provided on the head inside of the hollow cove at a point where the head contacts the arm, the pivots being constructed and arranged, when they are inserted into the grooves and rotated relative to the recesses into their operative position in the recesses, to prevent relative rotational movement between the arm and the head. 